I recently had some issues with my AirPort Extreme, and it appeared to have given up on itself. I thought it might be useful to share the steps I went through which eventually got it back working.
The first sign was the WiFi network going down. The Extreme is in a studio, connected via wifi to a modem in the main building. AirPort Utility indicated the internet was down, so I restarted the modem and the network (main building) was working fine. Still no luck on the Extreme.
A factory restore led to the same outcome. I tested the ethernet through direct connection to a MacMini (a pain as it is run headless). I subsequently connected my MacBook Pro (Touchbar) directly to the ethernet cable from the main building via my OWC Thunderbolt 3 dock.
I tried the Extreme another time, with the MBP connected to the Extreme via ethernet. The indicator light went green briefly (and webpages loaded) before it went orange and no net connection again.
I tried another factory restore, with the same result.
Fortunately, I had an Airport Express sitting in the cupboard and I used this to get my WiFI network back up (including installing the recent firmware update). I thought it worth connecting the Extreme to the Express (via ethernet) and giving it another try. Some magic happened…
I switched out the Express for the Extreme and it has not since skipped a beat. I also installed the latest firmware on the Extreme.
Worth noting, the day the Extreme went down was quite a warm one here and it might have cooked a little. Will keep an eye on it…